Demonstration of a novel 2.0 mm x 1.6 mm x 0.9 mm PCS Tx filter with steep pass band rolloffs & high rejection

Abstract

Improved process control of a Thin Film Bulk Acoustic (FBAR) resonator process has enabled the development of a low cost, high performance transmit filter capable of replacing the existing dual-filter "split-band" solution used in many PCS communication systems today. This transmit filter, centered at 1880 MHz, meets seven stringent specification requirements over a temperature range from -30C to +85C: (1) insertion loss < 3.5 dB over a 60 MHz (3%) bandwidth, (2) above band rejection > 35 dB over the 60 MHz (3%) rx band, (3) below band rejection > 25 dB over the 60 MHz (3%) image band, (4) low-frequency rolloff <9.0 MHz (from 3.5 dB to 25 dB), (5) high-frequency rolloff <8.0 MHz (from 3.5 dB to 35 dB), (6) bluetooth rejection (at 2.5 GHz) >30 dB and 2 nd harmonic rejection (at 3.8 GHz) > 20 dB, and (7) an in-band return loss better than 10 dBs. We present a novel filter design packaged in a 2.0 mm x 1.6 mm x 0.9 mm chip-on-board package, which meets these constraints. We discuss the process control requirements needed to produce this filter with high yields.